Re: [PATCH v4 4/4] media: uvcvideo: defer streaming restart after hibernation snapshot

[Alan Stern]

On Wed, Jul 29, 2026 at 04:43:44PM +0200, Oliver Neukum wrote:
> On 29.07.26 16:08, Alan Stern wrote:
> 
> > You're missing an important fact: If something goes wrong during the
> > hibernation transition (for example, if the kernel's memory image can't
> > be stored to disk) then there will be no RESTORE phase.  Following the
> > THAW phase, the system will return to normal operation.
> 
> Right, but that does not need to mean that the driver has to be operational
> at the THAW phase. It has to be operational before userland is unfrozen
> again at the latest. The difficulty how the driver learns that the system
> will not power down remains to be solved.
> > For this reason, during THAW drivers must not assume that the system is
> > about to power down.
> 
> True. For this reason the patch introduces a notifier queue.
> 
> Now, that you make me think about that it seems to be inelegant, as this throws
> away the proper order of the device tree. It seems to me that we should
> bite the bullet and go for the big solution:
> 
> Split the THAW phase in two, like a THAW_WRITEOUT and an optional
> THAW_BAILOUT that is called only when the system does not power down.

I could think up some better names for it.  Also, it doesn't fit into 
the existing scheme of callbacks, whereby each "suspend"-type callback 
has a corresponding "resume"-type callback.  The new one you're 
proposing would be something different -- a "stay-alive" callback, 
neither suspend nor resume.

Alan Stern